Inglês

Read the text below and answer questions 44 and 45.

Modulation is the process of transforming a message

signal to make it easier to work with. It usually

involves varying one waveform in relation to another

waveform. In telecommunications, modulation is used

to convey a message, or a musician may modulate

the tone from a musical instrument by varying its

volume, timing and pitch. In radio communications for

instance, electrical signals are best received when the

transmitter and receiver are tuned to resonance.

Therefore, keeping the frequency content of the

message signal as close as possible to the resonant

frequency of the two is ideal. Often a high-frequency

sinusoid waveform is used as carrier signal to convey

a lower frequency signal. The three key parameters of

a sine wave are its amplitude (volume), its phase

(timing) and its frequency (pitch), all of which can

be modified in accordance with a low frequency

information signal to obtain the modulated signal.

A device that performs modulation is known as a

modulator and a device that performs the inverse

operation of modulation is known as a demodulator

(sometimes detector or demod). A device that can do

both operations is a modem (short for ModulatorDemodulator).

Fonte: http://en.wikipedia.org/

Select the statements that are true for Modulation according to the text. I.The process of transforming a message signal to make it easier to work with is also known as waveform. II.One of the uses of modulation is to convey a message. III.The three key parameters of a sine wave are its amplitude, its phase and its frequency. IV.In order to obtain a modulated signal the key parameters of a sine wave can be modified in accordance with a low frequency information signal.